During the integrated circuit (“IC”) manufacturing process, contaminants, such as particles, photoresist residue and the like, are introduced on the IC substrate surface. It is important to eliminate or reduce the presence of these contaminants as they adversely impact the performance and function of the IC that is ultimately produced. Accordingly, various cleaning methods have been implemented to remove such undesirable contaminants.
A cleaning method commonly used in the semiconductor industry employs a concentrated ammonium hydroxide solution known as the Standard Cleaning Solution 1 (the “SC-1 solution”). In the SC-1 solution, typically heated ammonium hydroxide, hydrogen peroxide and deionized water are present in a volume ratio of approximately 1:1:5. During cleaning, the SC-1 solution contacts the substrate surface in the presence of megasonic energy. It is believed that the SC-1 solution detaches contaminants from the substrate surface through surface etching and that the megasonic energy further removes the detached contaminant from the substrate surface. Although this method has been the cleaning method of choice for most in the semiconductor industry during the last forty years, it suffers from several drawbacks.
Concentrated cleaning solutions run the risk of unduly etching, which appears as surface roughness, and thereby damaging the substrate surface and the devices undergoing cleaning. In a non-patterned semiconductor substrate surface, for example, over etching damages the real estate on the substrate surface, upon which circuitry and transistor devices are subsequently fabricated. For this reason, the resulting semiconductor chip may suffer from poor electrical performance or complete malfunction.
Dispensing highly concentrated cleaning solutions to drain poses environmental concerns. Consequently, the concentrated effluent stream exiting the cleaning system requires appropriate treatment. The cost of an effluent treatment system and labor to implement the cleanup process make the process of cleaning using the SC-1 solution expensive.
Concentrated cleaning solutions also deposit on the substrate surface undesirable metal contaminants which degrade device performance. Moreover, the peroxide composition of the cleaning solution typically contains stabilizers, which is another source of contamination that leads to performance issues. This problem is further exacerbated when relatively high composition of peroxide is used as part of the cleaning solution.
The presence of such contaminant particles even more adversely impact current IC geometries. With the miniaturization of the circuitry on ICs, device sizes are currently approaching progressively smaller scales and such small devices densely populate the IC substrate surface. Contaminant particles of a certain size, which previously did not pose a threat to an IC's performance because the early generation ICs were not as densely populated, now have a significant impact on the electrical performance of current ICs having miniature geometries. In fact, these contaminant particles can render the entire IC useless. As a result, an effective cleaning method for removing such contaminant particles, without damaging the substrate surface, is critical to enhancing the yield of ICs.
In an attempt to circumvent the above-mentioned drawbacks, U.S. Pat. No. 6,681,781 issued to Puri et al. proposes a cleaning solution formed from ultra dilute concentrations of a cleaning enhancement agent (e.g., ammonia gas) in a solvent (e.g., water). In ultra dilute solutions, the solvent and solute are present in volume ratios ranging from 500:1 to 500,000:1. Unfortunately, this process also suffers from drawbacks.
At the high end of ultra dilute ammonium hydroxide concentrations, the reaction of ammonium hydroxide with silicon continues to produce over-etched surfaces in the current IC geometries. To minimize drawbacks of over etching, an ozonating step has been added to the cleaning process. As a protective measure, in this step, the substrate surface undergoes ozonation before it is exposed to the cleaning solution containing a harsh concentration of ammonium hydroxide. Such an additional step, however, lowers the throughput of the cleaning process and the throughput of the overall IC manufacturing process. It also adds to the expense of cleaning the substrate surface.
At the low end of ultra dilute ammonium hydroxide concentrations, the cleaning solutions are simply not effective to detach the contaminant particle from the substrate surface. In other words, cleaning solutions having low concentrations of ammonium hydroxide do not sufficiently react with the substrate surface to detach a desirable amount of contaminant particles from it. Conventional wisdom, as a result, deems cleaning solutions having low concentrations of a cleaning enhancing agent, such as ammonium hydroxide, to be ineffective and undesirable.
What is therefore needed are improved systems and methods of cleaning ICs, which do not suffer the drawbacks of the current IC cleaning processes and effectively clean IC substrate surfaces having the current miniature geometries.